In the foodstuff industry strict requirements are imposed on valves especially as regards the cleanability and hygiene of the valve, in addition to conventional, structural and quality requirements. At present a great variety of valves are known for use in connection with the handling of different kinds of foodstuffs under various conditions. A recent development in this branch is represented by the valve disclosed in the U.S. Pat. No. 4,073,471, intended for use in handling foodstuffs, which is easy to clean in place and to control, in which endeavours have been taken to eliminate flow resistance, and in which the tightening of the valve may be conveniently accomplished by using a special tightening means.
Especially in certain countries the provisions concerning handling of foodstuffs raise problems which have not up to date found any satisfactory solution in spite of development work done. The washing of foodstuffs pipe systems in particular causes problems because the respective foodstuff liquid and the washing liquid, such as caustic solution for instance, have to be separated by at least two valves in order to safeguard against intermixing of liquids. So major economic values are also involved since even the smallest amount of washing liquid entering the foodstuff liquid through a leaking valve might spoil the product simultaneously in process. It follows that as a rule certain pipe systems have to be built using a unit of two valves as a basic building element to minimise the probability of the mixing of foodstuffs and e.g. washing liquids. This naturally implies considerably increased initial costs as well as increased operating and maintenance costs.
The cause responsible for the drawback mentioned is that no one has so far been successful in developing a hygienic as well as economic shut-off valve for foodstuff liquids in which positively no leaks would occur, and in which the leaks occurring could be observed e.g. in the washing situation, when the valve separates the foodstuff from the washing solution.
The object of the present invention is to eliminate the drawbacks mentioned above. The features characterized of the invention have been presented in the claims.